1. Field of the Invention
The present invention is generally related to a method for controlling an internal combustion engine and, more particularly, to a method for controlling the temperature of air flowing from a supercharger to an intake manifold of the engine for the purpose of improving the operating characteristics of the engine and preventing disadvantageous condensation within components of the air intake system.
2. Description of the Prior Art
Those skilled in the art of internal combustion engines and particularly marine propulsion systems are familiar with the use of superchargers in conjunction with the air induction system of the engine and, in some cases, the use of charge air coolers to reduce the temperature of the compressed air provided by the compressor, or supercharger.
U.S. Pat. No. 6,378,506, which issued to Suhre et al. on Apr. 30, 2002, discloses a control system for an engine supercharging system. A bypass control valve is controlled by an engine control module as a function of manifold absolute pressure and temperature within an air intake manifold in conjunction with the barometric pressure. An air per cylinder (APC) magnitude is calculated dynamically and compared to a desired APC value which is selected as a function of engine operating parameters. The air per cylinder value is calculated as a function of the manifold absolute pressure, the cylinder swept volume, the volumetric efficiency, the ideal gas constant, and the air inlet temperature. The volumetric efficiency is selected from stored data as a function of engine speed and a ratio of manifold air pressure to barometric pressure.
U.S. Pat. No. 6,405,692, which issued to Christiansen on Jun. 18, 2002, discloses an outboard motor with a screw compressor supercharger. An outboard motor is provided with an engine having a screw compressor which provides a pressurized charge for the combustion chambers of the engine. The screw compressor has first and second screw rotors arranged to rotate about vertical axes which are parallel to the axis of a crankshaft of the engine. A bypass valve regulates the flow of air through a bypass conduit extending from an outlet passage of the screw compressor to the inlet passage of the screw compressor. A charge air cooler is used in a preferred embodiment of the bypass conduit that extends between the cold side plenum of the charge air cooler and the inlet of the compressor. The bypass valve is controlled by an engine control module in order to improve power output from the engine at low engine speeds while avoiding any violation of existing limits on the power of the engine at higher engine speeds.
U.S. Pat. No. 6,408,832, which issued to Christiansen on Jun. 25, 2002, discloses an outboard motor with a charge air cooler. The outboard motor is provided with an engine having a screw compressor which provides a pressurized charge for the combustion chambers of the engine. The screw compressor has first and second screw rotors arranged to rotate about vertical axes which are parallel to the axis of a crankshaft of the engine. A bypass valve regulates the flow of air through a bypass conduit extending from an outlet passage of the screw compressor to the inlet passage of the screw compressor. The charge air cooler improves the operating efficiency of the engine and avoids overheating the air as it passes through the supercharger after flowing through the bypass conduit.
U.S. Pat. No. 6,508,233, which issued to Suhre et al. on Jan. 21, 2003, discloses a method for controlling a fuel system of a multiple injection system. A method for controlling a fuel system of a multiple injector engine provides a primary fuel injector and a secondary fuel injector which are both connected in fluid communication with an air stream flowing to a combustion chamber of the engine. Based on the total magnitude of fuel required to be injected into the air stream and as a function of the engine speed and percent load of the engine, first and second shares of the total magnitude of fuel are determined for the primary and secondary fuel injectors. The primary and secondary fuel injectors are then caused to inject their respective shares of the total fuel magnitude into the air stream, with the primary and second shares being determined as a function of engine speed and percent load of the engine.
U.S. patent application Ser. No. 10/300,766, which was filed by Roithinger on Nov. 21, 2002, describes a cooling system for an internal combustion engine. The cooling system is intended for use with an engine having a two-stage supercharging system. It includes a charge air line in which are provided a first compressor of a first turbo charger and a second compressor of a second turbo charger downstream of the former. A first charge air cooler is provided between the first and second compressors. A second charge air cooler is provided downstream of the second compressor. At least one of the two charge air coolers is disposed upstream of the coolant cooler as seen in flow direction of the cooling air, wherein the second charge air cooler is disposed above or beside the first charge air cooler.
U.S. Pat. No. 6,561,169, which issued to Sealy et al. on May 13, 2003, describes a charge air management system for an automotive engine. The system provides air charge densification and cooling during periods of operation at higher load. Two air ducts are provided, with a first for furnishing uncooled and unboosted air, and with a second duct for furnishing chilled and boosted air, with the second duct being chilled during operation with air flowing through the first conduit.
U.S. Pat. No. 4,207,848, which issued to Dinger et al. on Jun. 17, 1980, describes a charging air heat exchanger installation. The system is intended for charging air of a low compression reciprocating piston internal combustion engine operating with exhaust gas turbo supercharging, which is equipped with a first charging air water heat exchanger that during the starting and partial load operation supplies the heat energy of a heater device to the charging air and which can be connected to the cooling water circulation of the internal combustion engine, and with a second charging air water heat exchanger which is connected to the cooling water circulation external to the engine; the two charging air water heat exchangers are thereby adapted to be traverse in parallel by the charging air while a control system enables a stepless control of the charging air flow through the individual heat exchangers as a function of the temperature of the charging air upstream of the cylinders and the operating condition of the internal combustion engine.
U.S. Pat. No. 6,394,076, which issued to Hudelson on May 28, 2002, describes an engine charge air cooler. The system includes a charge air compressing system, a refrigerant cycling system, and a charge air cooling apparatus for transferring heat from the compressed charged air of the charge air compressing system to the refrigerant fluid of the refrigerant cycling system. The charge air cooling apparatus comprises a housing with a charge air passage for charge air moving through the housing. A plurality of fins are positioned in the charge air passage. A fluid tube is provided in the housing and passes through each of the fins in a plurality of locations.
U.S. Pat. No. 6,460,337, which issued to Olofsson on Oct. 8, 2002, describes a combustion engine. A turbo-fed internal combustion engine has a first and a second exhaust gas valve per cylinder, these exhaust gas valves each being connected to their respective exhaust manifold. One exhaust manifold conducts exhaust gases to an exhaust gas turbine and the other exhaust manifold conducts subsequent exhaust gases past this exhaust gas turbine which drives a compressor for charge air. The intake valve of the cylinder is arranged so as, as the engine speed increases, to close either earlier, before the piston reaches its bottom dead center, or later, after the piston has past its bottom dead center. In this way, the temperature increase resulting from compression in the cylinder is reduced. Cooled air from the compressor can be taken in so as to obtain an adequate degree of filling in the cylinder, with a lower final temperature.
U.S. Pat. No. 5,394,854, which issued to Edmaier et al. on Mar. 7, 1995, describes a cooling system for a supercharged internal combustion engine. The cooling system has a high temperature and a low temperature circulating system, in which two charge air coolers, through which coolant for different temperature level flows, are provided for cooling the charge air in two stages. The high temperature circulating system comprises a main branch with the internal combustion engine and a high temperature recooler which is connected in series with it. So that the total quantity of coolant may be kept low and a high degree of heat exchange can be achieved while the arrangement of the pipes is simple, the coolant quantity flowing out of the secondary circulating system is admixed to a coolant flow leading to the internal combustion engine, and the total coolant flow flowing out of the internal combustion engine is then guided to the high temperature recooler. The coolant quantity required in the secondary branch is branched off the coolant flow flowing to the internal combustion engine which flows away from the high temperature recooler and to which coolant quantities are possibly admixed that flow away from the high temperature charge air cooler and from the low temperature charge air cooler and from the low temperature charge air cooler. The low temperature circulating system comprises a low temperature recooler with a series connected low temperature charge air cooler.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
When a supercharger is used in conjunction with an internal combustion engine of an outboard motor, the air compressing action of the supercharger raises the temperature of air flowing through the supercharger as that air is compressed and flows from the supercharger outlet. In certain applications, a charge air cooler is used to reduce the temperature of the compressed air flowing from the supercharger. This cooling has the effect of increasing the density of the compressed air and, therefore, the operational capability of the internal combustion engine in which that compressed air is used.
When the engine is operating at low loads and speeds, the availability of compressed air is less advantageous than when it is operating at high loads and speeds. When the supercharger, such as a screw compressor, is deactivated or operated in a way that results in less work being done to compress the air, the effect of a heat exchanger, which cools the air from the supercharger, can result in deleterious conditions. As an example, the cooled air from the heat exchanger can reduce the percentage of suspended fuel in the air/fuel mixture that is in a vapor state as it passes into the cylinders of the engine. If the air flowing into the intake manifold of the engine is at a temperature lower than its optimum temperature, fuel efficiency and exhaust emissions can also be significantly compromised.
It would therefore be beneficial if a system could be provided that regulates the temperature of air passing into the intake manifold as a function of the operating characteristics of the engine so that a heat exchanger can be used to reduce the temperature of compressed air when this reduction in temperature is advantageous, but also to decrease the effect of the heat exchanger when the cooling of the compressed air is not beneficial.